Physical interface modules, such as the ‘enhanced Small Form-factor Pluggable’ module (SFP+), the ‘Quad Small Form-factor Pluggable’ module (QSFP) and the ‘120 Gb/s 12x Small Form-factor Pluggable’ module (CXP) are compact, hot-pluggable transceivers used for both telecommunication and data communications applications. Physical interface modules are typically used to interface a network device to a fiber optic or copper networking cable.
Some physical interface modules such as the SFP+ are hot-swappable electronic components that have an electrical interface toward the electronic device being interfaced with the network, and a specific copper or optical interface toward the network. SFP+ modules are widely used because of their hot-swappable characteristic, which means that they are replaceable at run-time without having to shut down the system. While preserving the same electrical interface with the electronic devices, several different copper or optical interfaces are typically used toward the network. Such flexibility has resulted in widespread adoption of hot-pluggable SFP+ modules by network operators.
There are different variants of physical interface modules, mainly depending on required bandwidth, speed, power and distance of the interconnection. While there are several variants of physical interface modules, each variant typically has the characteristic of being pluggable at the edge of electronic cards, boards or boxes. Once the physical interface module is inserted at the edge of the device, a networking cable can be connected to the physical interface module.
Active optical cables (AOC) are similar in concept to physical interface modules, and are typically located at the edge of an electronic card, board or box. An AOC reuses the same electrical interface as an already existing physical interface module, such as a QSFP module, as well as the same cage located on the electronic equipment, normally meant for a physical interface module. One of the main differences between a physical interface module, such as a QSFP module, and an AOC-based QSFP is that the AOC does not provide a standardized networking interface, only a standardized electrical interface toward the electronic device. For example, in the case where the AOC vendor provides an optical signal at a specific non-standardized wavelength, then only that vendor can interconnect with its own equipment.
Both ends of an AOC cable are terminated with a physical interface module. Both modules are inseparable from the cable. An optical engine is included in each connector of the AOC. Each optical engine converts signals between the electrical and optical domains.
By using standardized physical interface modules and AOCs, it is possible to develop electronic equipment, such as servers, switches and routers, with the option of leaving to the network operators the task of carefully selecting the required network interface at deployment time. While this approach has several advantages, there are a few optimizations that can be considered in order to better address the increasingly important challenges concerning footprint and energy consumption.
For example, a large part of the energy consumed by a physical interface module located on the edge of a board, such as a CXP module or an AOC, is used for interfacing the electronic components directly located on the same board. That means that modules located on the edge of cards or boards could greatly reduce their power consumption if the length of electrical traces between electronic components on the board, such as an ASIC (Application Specific Integrated Circuit), and a physical interface module located on the edge is significantly shortened.
Also, physical interface modules are typically designed for flexibility and interoperability which normally results in a corresponding form-factor which is not necessarily optimized in terms of size. For example, the same QSFP physical interface module can be used for short-reach and long-reach applications. While the long-reach variant requires significantly more power than the short-reach variant, the form-factor specification for the QSFP module is typically based on the required power consumption of the long-reach variant. Accordingly the size of a physical interface module is typically much larger than what is minimally required.
More recently, optical engines have received wider use for interfacing electronic equipment. Optical engines are components used to convert electrical signals into optical signals, and vice-versa. Optical engines are typically required to be placed at a very close proximity to the source of the electrical signals to be converted into optical signals. While such close proximity minimizes the length of electrical traces, the complexity of electronic components typically required in CXP modules and AOCs can be greatly reduced by using optical engines, for example by eliminating the need for Clock Data Recovery (CDR) functions. Such reduced complexity brings smaller footprint and power savings.
Optical engines can be extremely small, and in comparison with an equivalent standardized physical interface module, optical engines can be smaller by an order of magnitude. While there are several different variants of optical engines, and there is currently no standardized form-factor and agreement for building them, optical engines are aimed at providing extremely efficient and optimized solutions in terms of energy consumption and footprint. However, currently there are no standards on the form-factor for optical engines. As such, optical engines from different vendors are not likely to be compatible.
Another conventional component found in optical-based networks is an optical fiber connector which terminates the end of an optical fiber. A connector mechanically couples and aligns the cores of fibers so that light can pass. Optical fiber connectors are used to join optical fibers when a connect/disconnect capability is required. In telecommunication and data communication applications, small connectors (e.g., so-called LC connectors) and multi-fiber connectors (e.g., so-called MTP connectors) are replacing more traditional connectors (e.g., so-called SC connectors), mainly to provide a higher number of fibers per unit of rack space.
A so-called MT connector, e.g. an MTP or MPO connector, can be used to interconnect up to 72 optical waveguides. The alignment of the optical fibers is possible because of the alignment pins available on the MT connector. In the case where multiple MT connectors are required, an array connector can be used to hold several MT connectors. Each MT connector has its own alignment pins, and additional alignment pins are provided for the array connector itself.
Current physical interface modules and AOCs are used to convert electrical to/from optical, not optical to/from optical. The use of optical engines instead of standardized physical interface modules can significantly reduce the footprint and power consumption of electronic circuit boards. Networking systems are increasingly required to become smaller and consume less energy, and therefore solutions based on optical engines are increasingly important in electronic board designs. Accordingly communications between electronic components located on the same board, or on different boards, must be done through the optical domain. However optical engines do not provide the flexibility and interoperability offered by standardized physical interface modules, nor a standardized form-factor. With the development of optical engines, optical signals will be driven directly from the PCB, and eventually directly from the ASIC devices. It will no longer be possible to selectively decide on the optical interface to use for interconnection, and a corresponding physical interface module for such optical engine based implementations is therefore desirable.